(1) Field of the Invention
The present invention relates generally to a printing substrate for signage and the like formed from a continuous fabric web and, more particularly, to a printing substrate formed and finished in a single operation which is substantially distortion free.
(2) Description of the Prior Art
Recent years have seen a proliferation of outdoor advertising media for such events as outdoor sporting events, concerts, celebrations, etc. As the volume of advertising has grown, so has the demand for more visible media which can be cost effectively produced quickly and with a high level of quality. Traditionally, printing substrates for such signage has been formed from woven fabrics because paper and non-woven fabrics are not strong enough for these applications. Woven fabrics can be produced as relatively large panels for use as banners and can be coated with print receptive materials that are resistant to running and fading of the printed materials. However, because of inherent problems with instability in the larger denier, high strength yarns needed and with fabric distortion created during the handling and subsequent coating of these fabrics, image quality often suffers in the form of streaking and uneven color absorption.
Knitted fabrics have heretofore not been suitable for use in outdoor signage because even higher degrees of distortion are usually introduced into a knitted fabric than a woven fabric as a result of movement and handling required to coat the knitted fabric in preparation for its intended use. However, knitted fabrics, if they could meet the required surface stability, would offer huge economic advantages over woven printing substrates. For example, warp knitting machines can produce large width continuous fabric webs at extremely high speed when compared to the speed of a loom. Fabric webs produced by warp knitting machines have many industrial applications but generally are subsequently coated with another material, such as plastic, to produce a composite material. In such cases, the fabric web acts as a substrate to give added strength and the plastic coating may be, for example, a roofing material. Because the fabric web is only used for reinforcement, distortion in the fabric web is not critical, nor is it usually seen by the end user.
While warp knitting machines having widths greater than 72 inches are common and relatively inexpensive, finishing machines having widths greater than 72 inches become exponentially expensive. In addition, the costs associated with moving such wide rolls of fabric can add substantial cost per yard to the final material. Prior art attempts to integrate the fabric forming and finishing operations into a single operation have not been very successful. Specifically, it is very difficult to control the thickness of the coating operation unless the coating operation is continuous. However, by its nature, fabric forming must be stopped and started when defects, such as broken yarns, occur.
Thus, there remains a need for a printing substrate for signage or the like formed economically from a weft inserted, warp knitted continuous fabric web while, at the same time, the fabric web can be finished in a single operation so as to be substantially distortion free for improved print quality.